1. Field of the Invention
The present invention relates to hybrid-type working machines and, more particularly, to a hybrid-type working machine having a plurality of electric loads.
2. Description of the Related Art
Generally, a hybrid-type working machine performs work by hydraulic pressure generated by a hydraulic pump, which is driven by an output of an engine (internal-combustion engine). The engine is efficiently operated by being assisted by an operation of a motor generator as an electric motor. The motor generator is mainly driven by electric power output from a battery. The battery, which is of a charge-discharge type, discharges electric power when assisting the engine. On the other hand, when the motor generator does not assist the engine, the motor generator serves as an electric generator by being driven by a power output from the engine. The electric power output from the motor generator, which is operated as an electric generator, is charged to the battery. Thereby, the battery is always maintained in a charged state in a certain extent so that the engine can be assisted by the motor generator driven by an electric power discharged from the battery.
Because the hybrid-type working machine is capable of assisting the engine by the motor generator, a maximum output of the engine can be reduced, which allows a small-size engine to be used. Additionally, when an output larger than the maximum output of the engine is requested by the hydraulic pump, such a request is met by assistance by the motor generator.
When the engine is assisted by the motor generator so that the request of the hydraulic pump is met, it is necessary to determine a power of the motor generator to output in order to assist the motor generator.
Japanese Laid-Open Patent Application No. 2007-290607 suggests a technique to correct a distribution ratio of a power output from a motor generator. In this technique, a hydraulic pump request power is acquired to determine the distribution ratio of the output power of the motor generator in response to the acquired motor power, and a difference between a target revolution speed and an actual revolution speed of an engine is acquired to correct the power distribution ratio in a direction to eliminate the difference.
A hybrid-type working machine is provided with not only a motor generator as an electric load but also other electric loads in many cases. For example, a hybrid-type hydraulic shovel is provided with electric loads such as a turning electric motor, a traveling electric motor, a lifting magnet, etc. Those electric loads are driven by electric power mainly supplied from a battery. However, an amount of electric power supplied by the battery is limited. If each of a plurality of electric loads requests a large electric power simultaneously, there may be a case where the requested electric power cannot be supplied sufficiently to all of the electric loads.
Thus, it is necessary to determine how to supply limited electric power to a plurality of electric loads when a total amount of electric power requested by the plurality of electric loads exceeds an available electric power.